ObjectivesInfancy represents a critical period for growth and development, and food insecurity during this time may impact later health. Few previous studies have assessed food insecurity and obesity in young children in the US, and even fewer have targeted infants. Moreover, the ability of federal food assistance programs to affect this relation remains unclear. MethodsWe examined 666 infants in the US-based Nurture birth cohort. We conducted home visits when infants were 3, 6, 9, and 12 months. We measured household food insecurity via maternal report using the US Household Food Security Survey Module: Six-Item Short Form. We categorized infants as living in full, marginal, low, or very low food security households. We calculated infant body mass index (BMI) z-score from measured lengths and weights using World Health Organization reference standards. We documented participation in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) and Supplemental Nutrition Assistance Program (SNAP) at each home visit. We used repeated-measures linear regression models with imputed data to examine covariate-adjusted associations between household food security and BMI z-score throughout infancy. ResultsNearly 70% of infants were black and 49% were female. At 3 months, 32.8% of infants were from households with low or very low food security. Infant BMI increased from months 3 to 12 in all food security groups (Figure). However, after adjustment for potential confounders, low household food insecurity (0.18; 95% CI 0.05, 0.32; P = 0.01) and very low household food insecurity (0.22; 95% CI 0.05, 0.38; P = 0.01) were associated with higher infant BMI z-score throughout infancy but marginal household food security was not (0.001; 95% CI −0.13, 0.13; P = 0.99). There was no evidence of effect modification by participation in either WIC (P = 0.36) or SNAP (P = 0.67). ConclusionsInfants from food insecure households had higher BMIs throughout infancy, and this association was not attenuated by WIC or SNAP participation. About one-third of infants in this cohort were living in food insecure households, which raises substantial concern from both a public health and obesity prevention perspective. Funding SourcesNIDDK, National Institutes of Health. Supporting Tables, Images and/or Graphs▪